1. Field of the Invention
This invention relates to metal cans, such as those which are in wide use for packaging soft drinks and other beverages. More specifically, this invention relates to an improved metal can, and especially a stylized, shaped can, that provides enhanced strength characteristics at a given container weight as compared with conventional metal containers.
2. Description of the Related Technology
Today's market for metal beverage cans is extremely price competitive, which necessitates making the cans from the least amount of metal possible while still providing the necessary structural integrity to prevent collapsing or wrinkling the container's side wall. Considering the enormous volume of cans that are made worldwide each year, even a small reduction of the amount of material that is necessary to provide a can of adequate strength promises substantial cost savings to the industry. Accordingly, a great deal of effort is being put into the development of metal cans having improved strength to weight characteristics.
It has been proposed to manufacture two-piece can bodies with circumferential, longitudinal or helical reinforcing ribs in order to impart additional column or crush strength to the can body wall. In particular, German published patent application DE 23 08 420 (1974) discloses formation of a can body with either helical and longitudinal ribs by means of a standard drawing and ironing technique wherein the punch is configured to create the additional thickness of the reinforcing ribs. A similar invention was the subject of published PCT application WO83/01916. U.S. Pat. No. 3,610,018 to Swanson et al. discloses manufacturing circumferential reinforcement ribs into a steel can body in order to increase the buckling resistance of a steel can.
Recently, there has been a great deal of interest in the can making industry about the possibility of manufacturing so-called "shaped" cans, which are configured to deviate from the standard "straight" or cylindrical shape. A shaped can might be attractive to a customer, for example, because it can suggest a beverage manufacturer's distinctive glass or plastic bottle designs, or other aesthetic or trade dress features. A shaped can is typically made from a cylindrical metallic preform, which is shaped and sized quite similarly to a standard straight or cylindrical can body. The metallic preform is forced into the desired shape by one of a number of different known methods, most of which use mechanical or gaseous pressure, or some combination thereof. A complete understanding of the deformation techniques for making shaped cans, which are still evolving, is not critical to an understanding of this invention.
Unfortunately, the shaping process tends to place a great deal of strain on certain localized areas of the can preform. Furthermore, any deviation from a cylindrical shape can reduce, among other things, the axial strength of the can. In addition, shaped cans tend to be more susceptible than straight cans to outward bowing or other deformation such as when they are internally pressurized by carbonation. The extent, location and type of deformation will depend on the specific configuration of shaped can. For example, one shaped can design with which the inventors are familiar has a portion that includes broad, inwardly extending generally longitudinal depressions or grooves which tend to be pushed outwardly under pressure. The conventional thought would be that this could and must be rectified by increasing the can's wall thickness. Doing that, however, would add to the customer's projected packaging expenses, making the can design less attractive to the final customer, who is usually the soft drink manufacturer or bottler.
A need exists in the industry for an improved metal can body and method of making that provides additional strength and deformation resistance to a can body, and especially to a shaped can body, without adding substantial weight to the can body.